Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and is associated with a dismal prognosis. Immunotherapy has demonstrated potential to generate durable antitumor activity in other types of cancer. In particular, agents that selectively target checkpoint molecules, such as anti-CTLA-4 and anti-PD-1 antibodies, have accelerated the field of cancer immunotherapy by directly combating the tumor's mechanisms of immune evasion. Notable results with these agents have already been reported in advanced melanoma, renal cell carcinoma, and lung cancer and trials are underway in GBM. Chemotherapy, which is part of the standard of care for patients with GBM, has been associated with immunosuppressive effects and with myeloablative results. Recent data from our laboratory shows that local chemotherapy may be a better alternative to systemic chemotherapy given that it avoids these untoward effects. The main goal of this proposal is to understand the main mechanisms by which GBM evades the immune system and how to thwart these mechanisms with local chemotherapy and checkpoint blockade to enhance an effective immune response against GBM. Our data demonstrates that local chemotherapy in combination with anti-PD-1 increases survival and provides an increase in memory T cells in an orthotopic glioma model and protects against tumor re-challenge. We propose to study: 1. Potential biomarkers of response in patients with GBM treated with LC and anti-PD-1 therapy as part of an ongoing clinical trial at our institution. 2. The neoantigen profile generated by LC in intracranial chemosensitive and chemoresistant murine gliomas, to determine the impact on TCR diversity and anti-tumor immune response. 3. The location and identity of APCs responsible for antigen presentation induced by LC. These data will have direct clinical relevance for the findings and can be translational into clinical trials and patient care. We expect that the data generated from these studies will provide novel insights into a previously unexplored aspect of chemotherapy and serve as a foundation for optimizing the efficacy of therapy and host immune function against GBM. The knowledge obtained from this study will undoubtedly result in better therapeutic alternatives for current unsuccessful treatment for patients with GBM.